1. Field of the Invention
The invention relates to a control apparatus and a control method for an internal combustion engine.
2. Description of Related Art
There is known a vehicle that is equipped with an internal combustion engine as a driving force source for running. For example, Japanese Patent Application Publication No. 2005-105885 (JP-2005-105885 A) discloses a hybrid vehicle that includes an internal combustion engine. This internal combustion engine is automatically stopped under a certain condition such as motor running or the like, and the stop position of a crankshaft is controlled by a motor-generator in consideration of the startability at the time when the internal combustion engine is restarted. In Japanese Patent Application Publication No. 2004-360549 (JP-2004-360549 A), as for an in-cylinder injection-type internal combustion engine having cylinders into which fuel is directly injected, there is described an art of controlling the stop position of a crankshaft through the generation of a braking force by burning the mixture in a cylinder during a compression stroke in stopping the internal combustion engine. In this in-cylinder injection-type internal combustion engine, ignition-based startup for rotating a crankshaft through the generation of a normal running torque by explosion is made possible by injecting fuel into the cylinder in an expansion stroke of the internal combustion engine that has stopped rotating, and igniting the fuel.
In a six-cylinder four-cycle internal combustion engine having cylinders into which fuel is directly injected, the crank angles of the respective cylinders are offset from one another by 120 crank angle (CA). Therefore, when the engine stops, a crankshaft is generally stopped at a crank angle at which a piston in any one of the cylinders is located at an intermediate position of an expansion stroke, which is advanced by, for example, 45 to 75 CA from a compression top dead center (TDC) as a top dead center after a compression stroke, due to a relationship between potential energy resulting from the pumping action (the action of something like a spring based on the compression of air) and a rotation inertia force. Thus, the ignition-based startup can be appropriately carried out. However, a stop at the TDC, namely, a stop of the piston in any one of the cylinders in the vicinity of the compression TDC may occur with a probability of about 5 to 10%. In this case, the crank angle of the cylinder in the expansion stroke (the cylinder located immediately in front of the cylinder with a stop at the TDC) is about 120 ATDC (a position advanced from the TDC by 120 CA), and an exhaust valve has already been open or will open soon. Therefore, a sufficient running torque is not obtained through ignition-based startup, so the execution of ignition-based startup may be substantially impossible. The aforementioned stop at the TDC is considered to occur due to friction of the engine or the like when the rotation inertia force and the pumping action are substantially balanced with each other. On the other hand, with a view to avoiding this stop at the TDC, it is conceivable to control the stop position of a crankshaft with the aid of an external force of a motor-generator or the like as is the case with, for example, the above-mentioned Japanese Patent Application Publication No. 2005-105885 (JP-2005-105885 A). It is also conceivable to cause a stop of rotation by burning the mixture in the cylinder in the compression stroke, as is the case with Japanese Patent Application Publication No. 2004-360549 (JP-2004-360549 A).